Crystalline thermoplastic polyester resins having excellent mechanical, electrical, physical and chemical properties and workability, such as polyalkylene terephthalate resins, are conventionally used as engineering plastics in the production of automotive parts and electric or electronic components. However, improved and/or special properties for polyester resins must be developed as a result of new end-use applications being proposed. In this regard, it is important in some high-temperature end-use applications for the resin to exhibit satisfactory thermal resistance properties (e.g., long-term thermal resistance). For example, the automotive industry requires that resins have excellent mechanical properties, particularly flexibility and toughness (such as impact resistance), at low temperatures and that these "low temperature" properties be maintained even during use at high temperatures for prolonged periods of time.
A technique for satisfying these requirements has been proposed wherein a thermoplastic elastomer, such as a polycarbonate, olefinic polymer or rubbery polymer, is incorporated into the thermoplastic polyester resin in combination with an epoxy resin or polycarbodiimide. Although polyester resins containing an elastomer and additives do exhibit (to some extent) improved mechanical properties, the resins are problematic since surface peeling usually occurs due to poor compatibility of the components. Thus, long-term thermal resistance of such conventional resins is insufficient. Further improvements have therefore been needed in this respect.
According to the present invention, polyester resin compositions are provided having excellent durability, particularly properties that are stable during use at high temperatures for prolonged time periods. These improvements have been made without impairing the otherwise excellent mechanical properties associated with polyester resins, particularly its toughness and moldability.
Broadly, the present invention relates to polyester resin compositions exhibiting long-term temperature resistance properties and to molded articles formed of the same which includes a polyester base resin comprised of a major amount of a crystalline thermoplastic polyester resin and a minor amount of a polyester elastomer, and an effective amount of an amide compound to impart long-term temperature resistance properties to the polyester base resin.
The present invention more specifically relates to a polyester resin composition comprising:
(A) between about 60 to 99 parts by weight of a crystalline thermoplastic polyester resin,
(B) between about 1 to 40 parts by weight of a polyester elastomer wherein the total of components (A) and (B) is 100 parts by weight, and
(C) between about 0.005 to 10 parts by weight of an amide compound of the general formula (I): ##STR2## wherein R represent an n-valent organic group, X represents an alkylene group having 2 to 10 carbon atoms or a substituted derivative thereof, Y represents --COOH, --OH, --SH or --NH.sub.2, and n represents an integer from 2 to 4, inclusive.
Further aspects and advantages of this invention will become more clear after careful consideration is given to the detailed description of the preferred exemplary embodiments thereof which follows.